(a) Field of the Invention
The present invention relates to a driving apparatus of a plasma display panel (PDP) and a method for displaying pictures on the plasma display panel, and more particularly, to a driving apparatus of a plasma display panel (PDP) and a method for displaying pictures on the plasma display panel which are capable of reducing pseudo contour.
(b) Description of the Related Art
Recently, flat panel displays, such as liquid crystal displays (LCDs), field emission displays (FEDs) and PDPs, have been actively developed. The PDPs are being preferred over the other flat panel displays with regard to their high luminance, high luminous efficiency and wide viewing angle. Accordingly, the PDPs are being highlighted as a substitute for conventional cathode ray tubes (CRTs) for large-screen displays of more than 40 inches.
The PDPs are flat panel displays that use plasma generated by gas discharge to display characters or images. The PDPs include, according to their size, more than several tens to millions of pixels arranged in the form of a matrix. These PDPs are classified into a direct current (DC) type and an alternating current (AC) type according to patterns of waveforms of driving voltages applied thereto and discharge cell structures thereof.
The DC PDP has electrodes exposed to a discharge space, thereby causing current to directly flow through the discharge space during application of a voltage to the DC PDP. In this connection, the DC PDP has a disadvantage in that it requires a resistor for limiting the current. On the other hand, the AC PDP has electrodes covered with a dielectric layer that naturally forms a capacitance component to limit the current and protects the electrodes from the impact of ions during discharge. As a result, the AC PDP is considered superior to the DC PDP with regard to a long lifetime.
FIG. 1 is a perspective view illustrating a part of an AC PDP. Scan electrodes 4 and sustain electrodes 5 covered with dielectric layer 2 and protective layer 3 are arranged in pairs in parallel on first glass substrate 1. A plurality of address electrodes 8 covered with insulation layer 7 is arranged on second glass substrate 6. Barrier ribs 9 are formed in parallel with address electrodes 8 on insulation layer 7 such that each barrier rib 9 is interposed between adjacent address electrodes 8. Phosphor 10 is coated on the surface of insulation layer 7 and on both sides of each partition wall 9. First and second glass substrates 1, 6 are arranged to face each other while defining discharge space 11 therebetween so that address electrodes 8 are orthogonal to scan electrodes 4 and sustain electrodes 5. In the discharge space, discharge cell 12 is formed at an intersection between each address electrode 8 and each pair of scan electrodes 4 and sustain electrodes 5.
FIG. 2 shows an arrangement of the electrodes in the PDP. The electrodes of the PDP are arranged in the form of an m×n matrix. m address electrodes A1 to Am are arranged in a column direction. n scan electrodes Y1 to Yn and n sustain electrodes X1 to Xn are alternately arranged in a row direction. Discharge cell 12 shown in FIG. 2 corresponds to discharge cell 12 shown in FIG. 1.
In general, a process for driving the AC PDP can be expressed by temporal operation periods, i.e., a reset period, an address period and a sustain period. The reset period is a period wherein the state of each cell is initialized such that an addressing operation of each cell is smoothly performed. The address period is a period wherein an address voltage is applied to an (addressed) cell to accumulate wall charges on the addressed cell to in order to select a cell to be turned on and a cell not to be turned on in the PDP. The sustain period is a period wherein sustain pulses are applied to the addressed cell, thereby performing a discharge according to which a picture is actually displayed.
As shown in FIG. 3, in the PDP, a gray scale is expressed by dividing one frame (1 TV frame) into a plurality of sub-fields and performing a time-division operation for the plurality of sub-fields. Each sub-field includes the reset period, the address period and the sustain period. FIG. 3 illustrates one frame divided into 8 sub-fields in order to express 256 levels of gray scale. As shown in the figure, each sub-field SF1-SF8 includes reset periods (not shown), address periods Ad1-Ad8 and sustain periods S1-S8. sustain periods S1-S8 have emission periods 1T, 2T, 4T, . . . , 128T of the ratio of 1:2:4:8:16:32:64:128.
For example, a level 3 of gray scale is expressed by discharging a discharge cell during a sub-field having an emission period of 1T and a sub-field having an emission period of 3T so as to have a total emission period of 3T. In this way, a combination of different sub-fields having different emission periods produce pictures of 256 levels of gray scale.
When input data of one frame of a picture input signal consists of 8 bits, it has values within a range of 0 to 255. Accordingly, input data having values of 127, 63, 31, 15, 7, 3, and 1 use only 7 (emitted in sub-fields SF1 to SF7), 6, 5, 4, 3, 2 bits and 1 bit, respectively. Remaining (non-used) bits are filled with “0” (i.e., not emitted in remaining sub-fields). Corresponding picture information is displayed depending on the number of sustain pulses defined by a level of automatic power control (APC). In other words, the picture information always uses all 8 bits irrespective of values of the picture information, that is, eight sub-fields are all operated. Also, in the case that a maximal value is small, high-order bits are merely filled with ‘0’.
When a moving picture is displayed according to the sub-field arrangement as shown in FIG. 3, pseudo contour is generated due to human visual properties. FIG. 4 is a diagram illustrating one example of the generation of the pseudo contour. If the moving picture having a level 127 of gray scale and a level 128 of gray scale in parallel moves to the right at a fixed speed, the pseudo contour may be exhibited as shown in FIG. 4 according to the sub-field arrangement shown in FIG. 3. According to a property that human vision catches up with the movement of the picture, the gray scale is perceived in an arrow direction as shown in FIG. 4. Accordingly, pseudo contour, such as a level 255 of gray scale, is generated between the level 127 of gray scale and the level 128 of gray scale.